Plaster applicator



March 6, 1956 E. J. HAzx-:N

PLASTER APPLICATOR 5 Sheets-Sheet 1 Filed May ll, 1954 Si L.

ATTOR/Vd'y March 6, 1956 E. J. HVAZEN PLASTER APPLICATOR 5 Sheets-Sheet 2 Filed May 1l, 1954 FICLZ INVENTOR. 7A/MEQ J. /ZEN ATTO/@Alfy March 6, 1956 E. J. HAZEN PLASTER APPLICATOR 5 Sheets-Sheef. 5

Filed May 11, 1954 ATTORNEY INVENTOR. Erf/Mm J. fmzfw March 6, 1956 E- J, HAZEN 2,736,997

PLASTER APPLICATOR Filed May ll, 1954 5 Sheets-Sheet 4 FIG.6

A-J BY MMM VEN TOR.

J HAZEN March 6, 1956A E. .1.l HAzl-:N

PLASTER APPLICATOR 5 Sheets-Sheet 5 Filed May 11, 1954 ZIZ F'lGJO INVENTOR. 4 7H/VER J. /ZEIV BY g i ATTORIVY United States Patent 2,735,991 PLASTER APPLIeAfroR Ethmer J. Hazen, Ford City, Pa., assigner to Pittsburgh Plate Glass Company, Allegheny County, Pa., a corporation of Pennsylvania Application May 1954, Serial No. 428,996 8 Claims. (Cl. Sla-'262) The present invention relates to improvements in a method and apparatus for laying a bed of plaster on a horizontal surface. More particularly, the present inven- ,tion relates to a method and apparatus for continuously laying a uniform thin bed of plaster on a succession of moving tables which receive and hold large sheets of glass during the grinding and polishing operations in the conf tinuous process manufacture of plate glass.

In patent application Serial No. 262,415 of Eugene Hoyet, led December 19, 1951s,for Plaster Applicator, there is disclosed amethod and apparatus for depositing a bed of plaster on the tables used in the continuous grind.-A ing and polishing of rough glass to form polished plate glass. ln the method disclosed in the above-identified Hoyet applicatioma thin bed of plaster is deposited `on the upper surface of a'succession offlat tables mounted on cast iron rectangular cars coupled together to move along a track to provide a continuous elongated horizontal surface upon which glass is fixed during't'he grinding and polishing operations. The Hoyet apparatus imparts a continuous uniform film of water to the upper surface of the tables and subsequently deposits a lmeasured. quantity of dry plaster of Paris uniformly into the water deposited on the surface. The glass sheets are then laid on the plaster-water slurry thus formed. The plaster sets suh-` sequently to hold the glass firmly on the tables while the latter are conveyed beneath grinders and polishers which finish the exposed upper surface of the glass sheets. The glass sheets and plaster are removedifrom'the tables, the sheets turned over to expose their unfinished `surface and the above process repeated for the opposite glass surface.

According to the present invention, the operation of the Hoyet apparatus is' improved by adding certain ,features to improve lthe uniformity of thickness of the plaster bed upon which the glass sheetsare Alaid duringl the grinding and polishing operations.

One object of the present invention is to provide an improved method and apparatus yfor depositing a uniformly thick layer of plaster onto a at surface.v

Another object of the present invention is Ato provide an improved method and' apparatus for the continuous deposition of a uniform bed of plaster onto the moving abutting tables upon which glass sheets are fixed, then ground and polished.

rl`hese and other objects are accomplished by lfirst' depositing a uniform fiim of lime water solution on the upper surface of the moving tables, passing the tables under a hopper mechanism provided with aV powdered plaster feeding mechanism, a rotatable brush and a filter screen to insure uniform deposition of the dry plaster onto the uniform film of water in the manner similar to that described inthe above-identified Hoyet application,

and subsequently passing the plasterlime wa't'er slurry under a thin rubber 'curtainto improve the uniformity of thickness of the bed ofplast'er slurry. The glass sheets are thenmounted upon the smooth bed so formed before the plaster sets completely.

Suicient plaster must be provided to insure that there ICC is no contact between `the glass sheets and the metal tables kon which the sheets are conveyed. Since a thickness of only a few thousandths of an inch is sufficient for such purposes, Athe uniformity of plaster bed thickness is important in insuring-.uniform laying of the glass sheets ,upon the plaster as well as economy of operation, since the plaster must be removed after the polishing operation is completed and cannot be reclaimed.

A typical apparatus lfor providing a uniform bed of plaster accordance with the method of the present invention has been selected'for the purpose of illustration and is shown in the accompanying drawings wherein:

Figure 1 is an elevation of the machine from the side where the cars emerge after the plaster beds have been laid on the tables, portions of the structure being broken away in vertical section to disclose the construction and arrangement of the parts more clearly;

Figure 2 is an elevation looking toward the lefthand end of the machine as viewed in Figure l, on a somewhat larger-scale than Figure l;

' Figure 3 is a vertical section through the dry plaster of Paris applicator taken substantially on line 3--3 of Figure l, but on a larger scale;

Figure 4 is a view, partly in elevation, but mainly in longitudinal vertical section, through one end o f the ro: tary brush of :the dry plaster'- of Paris applicator, showing theA driving connection therefor, this view being taken substantially on line 4f4 of Figure 5,;

Figure 5 is a view taken substantially .on line 5.-5Aof Figure l., 'but to larger scale, showing the end bearing for the rotary .brush and means for vertical adjustment of the brush;

" Figure 6 is a view partly in plan and partly in horizontal section showing the driving connection for rotating the applicator brush and for simultaneously oscillating the 8448 of Figure 2;

Figure 9 is a schematic view of a circulating system for storing and circulating lime water before delivering l it to the lime water applicator;

Figure 10 is an enlarged elevational view of a filter used with the circulating system;

Figure l1 is a view similar to Figure 3 showing a portion of an alternate embodiment of the plaster of Paris applicator.

According to the present invention the lime water and the dry plaster of Paris are handled separately until they are brought into contact; with each other on the grinding and polishing tables forming the tops of the cars. The lime water and the dry plaster of Paris are deposited continuously on the tables. As the cars move along the track, successive increments of the moving tables are charged first with a measured amount of lime Water uniformly distributed over the table surface, and then with a measured amount'of dry plaster of Paris uniformly dis-Y tributed over the wetted surface. The plaster bed thus formed on thetable surface is smoothed by passing the mating the operation of applying grease? Referring first to Figures 1 and 2 of the drawings, the means for charging the table surfaces successively with water and dry plaster of Paris are supported by a framework which extends over the track along which the cars move. The rails of the track are designated 100, and 102 denotes a car, the table top 104 of which is to have a thin Ybed of plaster deposited thereon for supporting and holding a sheet of glass firmly on the table. These tables may vary in size in different installations, depending on the size of the sheets of glass which are to be ground and polished, but ordinarily will be uniform in size in any particular installation. Merely by way of example, they may be of the order of to 12 feet on a side. The direction of car movement is from left to right in Figure 2, as indicated by the arrow. In operation, a series of these cars are coupled closely together to form a substantially continuous elongated surface of uniform width which advances at a uniform speed under the water and plaster applicators and then, after sheets of glass have been laid on the plaster beds, to grinding and polishing apparatus. The speed of movement of the cars is usually in the range of about 8O to 200 inches per minute.

The framework for supporting the apparatus which de posits water and dry plaster of Paris on the tables is preferably of Welded steel construction. In the illustrative embodiment, this framework comprises two upright members 106 on each side of the track. The members 106 are secured at their lower ends to the floor, and are joined at their upper ends by beams 103 spanning the track, and by shorter beams 110 parallel to the track.

The apparatus for applying the dry plaster of Paris to the tables, indicated generally by the reference numeral 112, is mounted within this framework, supported by brackets 114; secured to cross members so that it is spaced a short distance above the top surface of the advancing tables. The apparatus for applying the water to the tables, designated generally by the reference number 116, is shown at the left-hand side of Figure 2, supported by the beams 118 which are secured at their lower ends to two of the uprights 106 and project outwardly and upwardly therefrom.

Between the water applicator 116 and the uprights 106, spanning the table top and supported by the uprights 106 and the beams 118, is a relatively narrow platform 120 providing a walkway for the operator of the machine. Conveniently, a similar walkway platform 122 is provided on the opposite side of the machine, supported by the other two uprights 106 and by the beams 123 which are secured at their lower ends to the uprights and project outwardly and upwardly therefrom. The supporting framework may include such additional supporting and reinforcing members as are desirable.

It will be seen from Figure 2 that as the cars 102 adi 'Y Vance along the track, the tables pass first under the apparatus 116 which deposits lime water thereon, and then under the apparatus 112 which deposits dry plaster of Paris onto the wetted table tops.

The function of the apparatus 116 is to charge successive mcrements of the tables 104 with a measured amount of lime water distributed uniformly across the table top as 1t advances under the apparatus. In the illustrative eme bodiment, the lime water is sprayed on the table surface, and preferably this is done by using one or more Hat-spraypattern nozzles arranged with the plane of the spray normal to the direction of movement of the tables. Ordinarlly, a more uniform distribution of the water can be obtained by using several spray nozzles spaced transversely of the table so that their spray patterns cover the entire width of the table without substantially overlapping. One or more spray nozzles are used depending on the width of the table, the height of the nozzles above the table top, the water pressure, and other factors.

The machine of the illustrative embodiment is designed for operation in three different 'ranges Vof table speeds.

The spray nozzles should be located a distance above the table which will insure substantially uniform distribution of water transversely of the table with a minimum of splashing and a minimum of movement of the water after it is deposited on the table. The greater the speed of the cars, the greater the volume of water which must be applied to the table in a given time interval. For reasons of economy it is desirable to use the same water supply and water pressure for all table speeds. Consequently, the spray nozzles which are to be used at the different table speeds have different How characteristics. It has been found desirable to locate the nozzles for the different table speeds at different heights above the table.

Ordinarily, it is desirable to use an accelerator such as potassium or sodium sulfate to shorten the setting time of the plaster of Paris, so as to permit a higher car speed, or a closer spacing of the plaster applicator to the grinding and polishing apparatus. There is a possibility that accumulation of lime from the lime water will gradually clog the spray nozzles. For that reason it may be desirable to have a standby set of spray nozzles for each table speed, so that in the event of any substantial diminution of water flow the standby set of spray nozzles can be substituted for those in use merely by actuating a suitable valve mechanism without interrupting the operation of the machine. The nozzles thus cut out of service can then be disconnected and removed from the water applicator 116 for cleaning, after which they can be replaced to serve as the standby set.

In the illustrative embodiment, two sets of spray nozzles are provided for each of the three ranges of table speeds for which the machine is designed, and each set comprises three spray nozzles spaced transversely of the table surface. It will be understood from the foregoing description that it is intended that only one set of spray nozzles will be in use at a time, and in a machine in which the table speed is kept within a narrow range a single set of spray nozzles may suice.

As can best be seen in Figure 2, the spray nozzles 124, intended for use at table speeds in the range of about to 130 inches per minute, are attached to the ends of short lengths of tubing depending from the supply manifolds 126, which extend transversely of the table and are connected at one end through suitable couplings and valves to a pipe supplying water under pressure. A separate manifold is employed for each set of spray nozzles. The spray nozzles 127, intended for use at table speeds in the range of about to 180 inches per minute, are attached to the ends of somewhat longer lengths of tubing 128, connected to the supply manifolds 129. The spray nozzles 130, intended for use at table speeds in the range of about to 225 inches per minute, are on the ends of still longer lengths of tubing 131, connected to the supply manifolds 132.

Preferably the supply manifolds 126, 129 and 132 rest in a rack 184 from which any one of them may be easily lifted when it becomes necessary to clean the spray nozzles. By attaching the spray nozzles 124, 127 and 130 on the ends of the lengths of tubing 12S, 128 and 131, respectively, rather than directly on the supply manifolds 126, 129 and 132, it is possible to locate all of the supply manifolds side by side in a single rack, while having the spray nozzles for different table speeds located at different heights above the table. By using flexible copper tubing for the connections 125, 128 and 131, it is possible to adjust the positions of the spray nozzles slightly relative to each other by bending the connections, so as to insure uniform distribution of the water transversely of the table.

As the coupled cars 102 move under the spray nozzles of the water applicator 116, successive increments of the tables 102 having a measured quantity of water deposited thereon, the quantity depending on the speed of the cars, the ow characteristics of the spray nozzles, and the water pressure. fljjhe quantity of lime water to be deposited on aus 9.-?

vms

the table surface is more than `the stoichiometric quantity required for reaction `with the subsequently applied dry plaster of Paris to cause it to set. The extra Water permits the plaster mix to iiow when the plaster bed is smoothed and also when the glass plate is laid thereon and rolled, so that no voids remain and a truly horizontal placement obtained. The lime water is evenly distributed transversely of the tables by the spray nozzles, so that the s entire table top is uniformly wetted as` it moves under` the liquid applicator.

The moving cars then carry the wet tables under the apparatus 112 which deposits a measured quantity of dry plaster of Paris on successive increments of the table surface. It is important that the wet plaster bed thus formed on the tables for receiving and holding sheets of glass be of .uniform thickness and consistency, so that the plaster will set quickly and uniformly, and so that the entire under surface of each sheet of glass is in direct contact with the plaster. To this end, the dry plaster of Paris should be deposited in a thin film distributed uniformly over the wet table top and smoothed in the manner described below.

Any splashing of water into the dry plaster of Paris as it is deposited on the table might result in the formation of lumps of plaster which, falling on the table surface and perhaps rolling thereon, would impair the uniformity of the plaster bed. Splashing of water from the spray nozzles or from the table top onto the dry plaster applicator mechanism might result in the accumulation thereon of Wet plaster which would be likely to break free from time to time and fall in lumps onto the table. In order to minimize these dangers, the water applicator 116 and the plaster applicator 112 are separated from each other by a spiash guard 133 which extends the full width of the moving tables, and from above the level of the spray nozzles to within a short distance of the surface of the advancing tables, for example about onefquarter inch. Conveniently this splash guard comprises a vertically arranged metal sheet which is disposed close to the spray nozzles of the water applicator. A similar splash guard may be disposed immediately ahead of the water appli-4 cator 116, as shown at'134.

Details of the construction of the dry plaster of Paris applicator 112 are disclosed in vl`i`rigures 1, 3 and 4 of the drawings. Spanning the line of advancing tables and spaced thereabove is a relatively narrow housing designated generally at 13.5. The length of this housing is slightly greater than the width of the tables. As seen in Figure 3, the lower part 13 6 of the housing substantially conforms to the peripheral contour of' a cylindrical brush 13S extending substantially the full length of the housing, and the side walls 137 of the housing extend ,vertically above the horizontal plane through the longitudinal axis of the brush. With the construction shown, spaces within the housing where dry plaster of Paris can accumulate and become packed into hard chunks are reduced toa minimum, and dry plaster of Paris fed onto the top of the brush, in the manner hereinafter described, `is carried around and down by the brush to be deposited on the tables.

In the bottom of the housing 135, extending the full width of the table surface, is a relatively narrow, wire mesh screen 139 through which the dry plaster of Paris is sifted onto the advancing tables. As ythe brush 138 rotates, the ends of the bristles move over the screen 139 and there is a peening action between the ends of the bristles and the wires of the screen. Thispeening action shakes loose the dry plaster vof Paris carried by the bristles and `causes it to drop through the screen onto-the tables advancing thereunder. This peening action is effective to prevent accumulation of impacted'dry plaster of Paris inthe brush, and an `even feeding of the dry plaster of Paris through the screen onto the table surface is made possible.

The screen 139 desirablyis stretched taut gin order to realize fully the peening effect .with the bristles. .In the embodiment illustrated in Figure 3, the longitudinal edges of the screen are permanently secured to cleat-like side members 141, which are clamped against the bottom of the applicator housing by a screen retainer 142 which is removably secured to the bottom of the housing, as by screws 144, Desirably the side members 141 of the screen and the screen retainer 142 are provided with cooperating beveled edges as shown at 143, so that as the screen retainer is drawn up against the bottom of the housing by the screws 144, the yretainer forces the side members apart to place the screen under tension.

If dry plaster of Paris is fed into the applicator housing 135 at a rate faster than it is discharged through the screen 139, the plaster of Paris may become impacted in the brush. Such lodging of plaster of Paris in the brush may resuit in an uneven discharge of the plaster of Paris through the screen, and also may require frequent cleaning of the brush. In order to minimize the likelihood of this happening, the dry plaster of Paris is fed intermittently in relatively small measured amounts directly onto the top of the rotating brush, and the brush bristles are arranged in spaced clumps as described in greater detail below.

As can be seen in Figure 3, the means for feeding the dry plaster of Paris onto the brush 138 comprises an open bottom bin 145 which is centered directly over the brush and extends the full width of the table surface. Preferably this bin yis substantially narrower than the diameter of the brush and its side walls are vertical so as to afford no spaces in which the dry plaster of Paris can accumul late and form into hard lumps.

Secured along the lower edges of the side walls of the bin 145, which extend downwardly to Within a short distance above the surface of the brush 13d, are scraper blades 146, 147 extending the full length of the bin. These scraper blades are vertically adjustable so that they can be made to clear the ends of the brush bristles, or so that they can be made to engage the ends of the bristles. Adjustability of the scraper blades is accomplished by means of vertically disposed slots 148 which fit over spaced, screw-threaded studs 149 mounted along the lower edges of the side walls of the bin 145, the scraper blades being clamped in adjusted position by wing nuts 150.

1f the tables are of the order of ten to twelve feet wide, and the scraper blade was made in one piece, it wouldbe virtually impossible for one man to adjust the blade with the requisite accuracy. In order to facilitate adjustment of the scraper blades by a single operator, the blades preferably are made not more than about two feet long, and are arranged in abutting end-to-end relation so as to pro-l vide continuous scraper edges extending the full length of the bin. The interior of the applicator housing 135 is reached for adjusting the scraper blades by lifting the hinge iiaps 151 which are mounted on the outer side Walls of the bin. The flaps, in lowered position, constitute a closure for the top of the applicator housing.

When the applicator brush rotates clockwise, as viewed in Figure 3, the scraper blade 146 preferably is adjusted so that the ends of the brush bristles impinge thereon. The resultant peening action dislodges plaster of Paris which has not fallen through the screen 139. At the same time, the scraper blade 147 desirablyl is adjusted so that there is a slight clearance between its edge andthe ends of the bristles, thus permitting a thin uniform layer of plaster of Paris to be carried on the surface of the rotating brush from the bin 145 to the screen 139, where it is scraped and shaken loose from the bristles and falls through'the screen onto the tables moving thereunder.

Dry plaster of Paris is fed intermittently in measured amounts onto the top of the brush 13S by a plaster gate located within the connection between the lower bin 145 and the upper bin 153. This plaster gate may comprise a shaft154 extending the fulllength of the b inand having a ,plurality @radially dspvsed blades Secured therese; as

by welding, located within a cylindrical housing formed at the adjoining portions of the lower bin 145 and the upper bin 153. When the machine is in operation, the shaft 154 is turned intermittently, always in the same direction, by a one-way rotary clutch 156 located outside of the bins at one end of the plaster gate. One type clutch is shown more or less diagrammatically, by Way of example, in Figure 7. Rotary motion of the outer shell of the clutch by the clutch actuating arm 160 in one direction will turn the shaft 154, while rotary motion of the shell in the other direction will not turn thc shaft.

Suitable clutch actuating and timing mechanism is provided to insure that the correct amount of dry plaster of Paris is fed onto the top of the brush. As shown, the actuating mechanism for the clutch is an air cylinder 157, the ram of which is pivotally connected to the clutch actuating arm 166, and the cylinder of which is pivotally secured at 151 to the framework which supports the plaster applicator. Operation of the air cylinder may be governed by a rotatable cam or a solenoid air valve and suitable electric timer control mechanism synchronized with the speed of rotation of the brush so as to supply the correct amount of dry plaster of Paris to the lower bin 14S for all operating speeds.

The upper bin 153 is izo-extensive in length with the lower bin 145, but preferably is made somewhat wider so as to provide storage space for dry plaster of Paris. The dry plaster of Paris may be fed mechanically to the upper bin, and in the drawings a motor driven screw conveyor 158 is shown for transferring dry plaster of Paris from a source of supply, not shown, to a point midway of the length of the bin, where it is discharged into the bin through a downspout 159. The dry plaster of Paris can be spread lengthwise of the upper bin manually, for example by a paddle handled by an operator of the machine standing on the platform 12d, thus insuring a continuous supply of plaster' of Paris along the entire length of the plaster gate 152. If for example, the tables are ll feet Wide, and the desired thickness of the plaster bed is .096 inch, and the table speed is 200 inches per minute, the quantity of dry plaster of Paris required is approximately 5.5 cubic feet per hour.

Details of construction of the cylindrical brush 138 are disclosed in Figures l, 3 and 4. As indicated hereinabove, the width of the tables may be of the order of l() to l2 feet. In order to ,attain a uniform discharge of dry plaster of Paris through the Vscreen across the full width of the tables, it is important that the brush be constructed so that there is minimum sag in the brush between its end bearings when the brush is in the applicator. The brush comprises a steel tube 162, on the ends of which the bristle holders 163 are secured rigidly. The bristles, made for example of nylon, are stili to insure effective peenin g action against the screen 139, and are arranged in spaced clusters about one inch apart around the tube so that the dry plaster of Paris deposited on the surface of the moving tables 1532 is not packed. The deposited plaster is carried largely by the outer ends of the bristles. The spacing of the bristle bunches enhances the peening eiect of the bristles against the scraper blade 146, which peening tends to inhibit caking of the plaster.

As the ends of the bristles move over the screen 139 they are bent slightly, and in the course of time the bristles may take a set which tends to lessen the peening effect and thus reduce the amount of dry plaster of Paris discharged through the screen. For this reason it is desirable that the driving mechanism for the brush be reversible, so that after the brush has been rotated in one direction until the bristles begin to acquire a set, the rotation of the brush can be reversed. When this is done it is necessary, of course, to reverse the adjustments of the scraper blades 146 and 147.

A more effective peening action between the bristles and the screen 139 is obtained with less tendency for the 8 bristles to acquire a set, if the brush is simultaneously oscillated along its longitudinal axis as it is rotated. As can best be seen in Figure 4, the brush holders 163 have substantially the same diameter as the outside of the brush and are rotatably supported in bushings 164, for example, graphited bronze, secured in the bushing end plates 165 (Fig. 5 so that the brush is free to move longitudinally as well as to rotate with respect to the bushing end plates. These bushing end plates are secured by cap screws 166 against the housing end plates 167 at the ends of the applicator housing 135. The driving mechanism for the brush will be described hereinafter.

Since the dislodgment of dry plaster of Paris from the brush and its uniform discharge through the screen 139 is dependent in part on the peening action between the bristles and the screen, it is desirable to be able to adjust the brush vertically with respect to the screen, both initially and as the bristles wear down. An arrangement permitting vertical adjustment of the bushing end plates 165 with respect to the housing end plates 167 is illustrated in Figures 4 and 5. The housing end plate 167 is provided at its top and bottom edges with outwardly projecting lugs 169, 17 which carry the vertical adjusting screws 171, 172, respectively. The

' ends of the adjusting screws 171, 172 bear against the top and bottom edges, respectively, of the bushing end plate 165. By loosening the cap screws 166, which pass through vertically disposed slots 163 in the bushing end plate 165, the bushing end plate can be adjusted vertically by means of the adjusting screws 171, 172. The screws 166 can then be retightened to hold the brush in its adjusted vertical position.

Details of the brush driving mechanism are disclosed in Figures l, 4 and 6. The driving connection to the brush is made to one end of the brush shaft 173 projecting beyond one of the brush holders 163, in which the shaft is rigidly secured. Firm secured on the outer end of the shaft 173 is a universal joint 174. The other end of the universal joint is rigidly connected to one end of a short shaft 175, which is rotatably mounted in thrust bearings 177 in one end of an elbow-shaped connecting arm 178. The shaft is driven, through miter gears 182, by the wrist pin 180 of crank 179.- The wrist pin is rotatably mounted in thrust bearings 181 in the other end of the elbow-shaped connecting arm 178, at right angles to the shaft 175. As shown in Figure 6, the Wrist pin 180 is offset with respect to the driving shaft 183, on which the crank is rigidly secured.

Upon rotation of the driving shaft 135, the rotation of the wrist pin 180 within its bearings in the connecting arm 178 rotates the shaft 175 and this in turn rotates the brush of the plaster applicator about its longitudinal axis. At the same time, the crank 179 causes the connecting arm 178 to oscillate toward and away from the end of the applicator housing 135, and the brush holders 163 slide as they rotate in their bushings 164. 1t is evident that this produces an oscillation of the brush 138 along its longitudinal axis as it rotates.

The driving shaft 183 preferably is reversible, so that the applicator brush can be driven in either direction. Desrably, the speed of the driving shaft is variable, so that the amount of dry plaster of Paris deposited on successive increments of the advancing table surface can be readily adjusted to the table speed. Conveniently the driving means 185 is a reversible electric motor embodying a variable, speed reducing mechanism which can be adjusted to produce the desired shaft speed, which is in the range of about 4 to 20 R. P. M. for the machine of the illustrative embodiment. One suitable drive is the Varidrive motor manufactured by U. S. Electrical, Inc.

Beyond the plaster applicator 112 is provided a wiping curtain 190. This wiping curtain is a rubber sheet extending completely acrossv the upper surface 104 of the'table 102. One longitudinal side of the wiping curtain is fixedly secured between, a .pair of securing plates 192 and 194, which, in turn, are mounted on a flange 196 on platform 122. The securing plates and the platform extend across the entire width of the tables 102. The opposite longitudinal side of the wiping curtain is free to ride on the upper surface of the plaster slurry as the tables pass beneath the wiping curtain. The wip.- ing curtain has a width such that when it is suspended from its mounting adjacent the mounting flange VV196 it contacts the upper surface of the slurry along an area about 8 to 12 inches wide extending completely across the table. The wiping curtain 190 is preferably made of rubber approximately Ms thick andmay be provided with a thin plastic film 19.8 in contact with the slurry. Suitable materials for the plastic film include polyethylene and cellulose acetate having thicknesses up to about .010 and a length and width sufficient to cover the entire wiping curtain 190. The provision of the plastic film facilitates cleaning. The wiping curtain 190 provides a more homogeneous mixing and smoothing of the lime water and plaster, thereby preventing adherence of excessive plaster to the undersurface of the glass to be ground and polished. y

An additional advantage of the thin plastic film 198 is that the plastic film may be oiled without harmful effects, whereas the rubber curtain is affected adversely by contact with oil, thus rougheuing the surface contacting the plaster, which results in roughness and nonuniformity in plaster slurry thickness. The use of oil as a parting material between plaster and other substances to inhibit adhesion therebetween is well-known and is not claimed as my invention.

In order to insure that the lime water applied onto the moving tables is deposited as a clear solution, a circulating system such as shown in Figure 9 is employed. A lime water mixing tank 200 is located at floor level and a pump 202 provided to force the lime water solution through a pipe 204 to an overhead storage tank 206 where the pressure head forces the liquid through one of two valved pipes upwardly through one of two filter housings 208, each provided with a filter 210, into the proper pipe 126, 129 or 132, according to the speed of the moving tables. The upward flow of lime water through the filters 210 facilitates cleaning the filter by a subsequent gravity fiow of tap water through pipes 212, filters 210, filter housing 208, pipes 214, valves 216 and sewer lines 218.

The valves 216 are designed to open to one position to allow the flush water applied for cleaning the filters to drain downwardly past the filter 210 into a sewer line 218. Another valve position, used when the filters are not being flushed, allows recirculation of excess lime water solution to the lime water mixing tank 200 via pipe 220. A third position which allows no liquid fiow may also be provided for the Valve, if desired.

The details of the filter housing 208 and filter 210 are shown in greater detail in Figure l0. The filter 210 may comprise a 60 mesh brass screen 222 extending across the filter housing 208 and mounted between two reinforced rubber ring gaskets 224 which are joined together by fasteners 226 spaced about the periphery of the filter housing 208. The filter housing 208 may be made of unitary structure or may be split at 209 to facilitate replacement of the screen 222.

In operation, the coupled cars 102 advance along the track 100, passing first under the water applicator 116 which charges successive increments of the table with a measured amount of water distributed uniformly over the table surface, then under the plaster applicator 112, which charges successive increments of the wetted table surface with a uniform thin layer of dry plaster of Paris, and, finally under the wiping curtain 190, which improves the smoothness of the plaster slurry formed. The plaster bed thus formed on the continuously moving table surface is uniform in thickness and in consistency. :the vtables 'moveA from underthe plaster applicator, sheets ofglass are laid on the wet plaster bed and are carried by the cars to the grinding and polishing machines.

In the illustrative embodiment, all of the water is applied to the table surface, after which the dry plaster of Paris is deposited on the wetted table and the 'slurry smoothed. While this ist'he preferred arrangement, a part of the water could be applied after the dry plaster of Paris has been spread on the table, for example, by providing a second water applicator following the plaster applicator 112 but before the smoothing curtain 190.

Referring to Fig. 11, an ,alternate structure for the plaster feed mechanism is. shown. An open bottom bin 245, similar to bin shown in Fig. 3, ,is located beneath housing 253. A cylindrical member 254 extends longitudinally of the housing 245 at the top of the latter and is provided with spaced longitudinal grooves 255 for carrying increments of `powederd plaster of Paris from the upper bin 253 into'the lower bin 245, the plaster eventually being deposited upon the brush 238.

Occasionally, plaster is accumulated non-uniformly along the length of the brush. In order to modify any unevenness in plaster accumulation longitudinally of the brush, a series of abutting gate members 256 pivoted to a wall of the lower housing at 257 are provided for selectively damming the flowiof plaster ontoY the brush at selected localized areas above the length of the brush. A slidable arm 258 is pivoted at a pivot point 259 to the gate member for rotating the gate member into closed position (as shown in the solid lines of Fig. 9),. Lever arm 258 is notched `at 260 to maintain the Agate member 256 in closed position by engagement of the notch 260 with the wall of the lower bin 245 when no fiow of plaster is desired. The slidable lever arm 258 is' lifted so that its notch 260 is out of engagement with the bottom of a slot 261 in the wall of the bottom bin 245, thus enabling the lever arm to be slid to the dotted line posi tion. In this latter position, the gate member is spaced from the grooved cylindrical member, thus allowing free flow of the plaster. The surface of gate member 256 which faces the periphery of the cylindrical member 254 is arcuately shaped to insure proper valve action upon moving the gate member 256.

Another feature shown in Fig. ll is an alternate embodiment for making adjustable the scraper blades 246 and 247, the mechanical equivalent of scraper blades 146 and 147 of Figure 3. In this embodiment, the scraper blades are mounted on mounting brackets 248 pivoted about hinges 250. Handles 251 are provided for selectively moving the scraper blades 246 and 247 into or out of engagement with the rotating bristles. that as the brush is rotated counterclockwise as seen in Figure 9 only scraper blade 246 contacts the bristles and upon clockwise rotation of the brush, only scraper blade 247 contacts the bristles. This improves the peening action of the bristles against the scraper blades.

It will be evident from the foregoing description that a method and apparatus have been provided for continuously laying a uniform plaster bed on the advancing tables, and that the plaster bed is laid mechanically and without preliminary mixing of the water and the dry plaster of Paris.

It will be understood that the invention herein described may be modified and embodied within the scope of the accompanying claims.

What is claimed is:

1. In apparatus for continuously laying a bed of plaster on an elongated fiat surface comprising, in combination, first means for continuously advancing the elongated surface, second means bridging across said first means for depositing a uniform covering of water on successive increments of the advancing surface, and third means bridging across said first means beyond said second means in the direction of advancement of the elongated surface It is preferred lfor depositing a uniform lm of dry plaster of Paris on successive increments of the wetted surface, the improvement comprising means for smoothing the slurry, said improvement comprising a mounting member and a thin flexible curtain extending lengthwise completely across the elongated surface beyond said third means in the direction of advancement of the elongated surface, said thin flexible curtain being fixed at its upper extremity to said mounting member a distance above said elongated iiat surface that is less than the width of said curtain, whereby a portion of the curtain is free to drag on the upper surface of the deposited plaster.

2` In apparatus according to claim 1, wherein said ilexible curtain is provided with a thin film of plastic material on its surface adapted to contact the plaster slurry.

3. In apparatus as in claim l wherein said improvement comprises a mounting member and a thin rubber curtain having a thickness of approximately 14s" fixed to said mounting member lengthwise thereof above said elongated flat surface anda thin plastic lilm attached to said curtain so that it contacts the deposited plaster along an area about 8 to 12 vinches wide extending completely across said elongated flat surface.

4. In apparatus as in claim 1 wherein the means for depositing the uniform lm of dry plaster of Paris comprises a relatively narrow housing for containing dry pulverized plaster of Paris arranged transversely over the elongated surface, a sifting screen at the bottom of said housing, a rotary vane member extending completely across the housing in spaced relation above the screen, and a rotary cylindrical brush extending longitudinally of the housing below said vane member, the improvement comprising spaced clusters of bristles on said brush, the ends of the bristles providing contact with the upper sur- 12 face of the screen, whereby rotation of the vane member deposits the plaster substantially uniformly onto the brush and rotation of the brush causes application of a uniform film of dry plaster on successive increments of the wetted surface.l

5. In the improvement according to claim 4, wherein adjustable peening means is provided to contact the bristles to prevent agglomeration of'excess plaster on the bristles.

6. In the improvement according to claim 4, wherein a plurality of independently adjustable gate members are located in abutting relation immediately beneath the rotary vane member, the total length of the gate members extending the full length of the narrow housing, to provide means for controlling the flow of powdered plaster at any desired localized area ,along the length of the vane member.

7. In the improvement according to claim l, which includes a circulating system comprising a water storage means, pumping means, and recovery means.

8. In apparatus according to claim l, wherein the means for depositing a uniform solution of water comprises a lter housing through which the solution is passed upwardly prior to its deposit on the elongated surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,031,190 Liebau July 2, 1912 1,194,520 Lewis Aug. 15, 1916 1,631,203 Hitchcock June 7, 1927 2,212,351 Moran Aug. 20, 1940 2,363,631 Walters Nov. 28, 1944 

